This protocol is part of a larger study on the effects of growth factors on energy expenditure, body composition and skeletal muscle mass in older persons. During the past year, 67 healthy volunteers of 65 years old and over (39 men and 28 women) were admitted to the GCRC for an overnight stay to have a four hour infusion leucine and an indirect calorimetry. Volunteers have to complete 2 studies: one at week 0 and one at 26 weeks. This is a double-blind, randomized study that will be ending in September 1998, when 120 volunteers will have both protein turnover studies completed.